Ink jet ink composition and printing method

ABSTRACT

This invention relates to an ink jet ink composition comprising water, a humectant, and polymer-dye particles, wherein said polymer-dye particles comprise a colorant phase containing a water insoluble dye, and a polymer phase, said particles being associated with a water-dispersible polymeric co-stabilizer. This invention further relates to an ink jet printing method utilizing the above ink jet ink composition.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. Pat. No. 6,867,251, issuedMar. 15, 2005, entitled POLYMER DYE PARTICLES AND PROCESS FOR MAKINGPOLYMER DYE PARTICLES by Wang et al.; and Publication No. 2003/0119938,published Jun. 26, 2003 (now abandoned), entitled INK JET INKCOMPOSITION AND PRINTING METHOD by Wang et al.

FIELD OF THE INVENTION

This invention relates to ink jet ink compositions comprising novelco-stabilizer used to prepare polymer-dye particles. It further relatesto an ink jet printing method using said ink jet ink compositions.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by thedeposition of ink droplets on a substrate (paper, transparent film,fabric, etc.) in response to digital signals. Ink jet printers havefound broad applications across markets ranging from industrial labelingto short run printing to desktop document and pictorial imaging.

In ink jet recording processes, it is necessary that the inks being usedmeet various performance requirements. Such performance requirements aregenerally more stringent than those for other liquid ink applications,such as for writing instruments (e.g., a fountain pen, felt pen, etc.).In particular, the following conditions are generally required for inksutilized in ink jet printing processes:

-   (1) The ink should possess physical properties such as viscosity,    surface tension, and electric conductivity matching the discharging    conditions of the printing apparatus, such as the driving voltage    and driving frequency of a piezoelectric electric oscillator, the    form and material of printhead orifices, and the diameter of the    orifices;-   (2) The ink should be capable of being stored for a long period of    time without causing clogging of printhead orifices during use;-   (3) The ink should be quickly fixable onto recording media, such as    paper, film, etc., such that the outlines of the resulting ink dots    are smooth and there is minimal blotting of the dotted ink;-   (4) The printed image should be of high quality, such as having a    clear color tone, high density, high gloss, and high color gamut;-   (5) The printed image should exhibit excellent water fastness (water    resistance) and light fastness (light resistance);-   (6) The printed (ink) images should have good adhesion to the    surface of image receiving elements and should be durable and highly    resistant to physical and mechanical scratches or damages;-   (7) The ink should not chemically attack, corrode, or erode    surrounding materials such as the ink storage container, printhead    components, orifices, etc;-   (8) The ink should not have an unpleasant odor and should not be    toxic or inflammable; and-   (9) The ink should exhibit low foaming and high pH stability    characteristics.

The inks used in various ink jet printers can be classified as eitherdye-based or pigment-based. Pigment-based inks have some deficiencies.For example, pigment-based inks interact differently with speciallycoated papers and films such as transparent films used for overheadprojection and glossy papers or opaque white films used for high qualitygraphics and pictorial output. This results in images that have poor dryand wet adhesion properties and that can be easily smudged.

Another deficiency from which pigmented inks suffer is their poorstorage stability due to the presence of a water-miscible organicsolvent. Water-miscible organic solvents are used to adjust inkrheology, to maximize ink firability, and re-runability. These solventsprevent ink from drying in a printing head and lower ink surface tensionto minimize the effect of air-entrapment in an ink formulation. Such airentrapment generates air bubbles which can seriously affect the headperformance. Unfortunately, these water-miscible organic solvents canalso have a negative effect on the colloidal stability of pigmentparticles in an ink formulation.

A dye is a colorant which is molecularly dispersed or solvated by acarrier medium. The carrier medium can be a liquid or a solid at roomtemperature. Known ink jet inks generally comprise a water soluble dyewhich is soluble in an ink vehicle such as water or a mixture comprisingwater and a known water soluble or water miscible organic solvent. Inkscomprising these soluble dyes may exhibit many problems, such as lowoptical densities on plain paper, poor water fastness, poorlightfastness, clogging of the jetting channels as a result of solventevaporation and changes in the solubility of the dyes, dyecrystallization and ink bleeding. There is a need to develop a waterresistant dye-based ink and to improve the existing inks. Morespecifically, there is a need to develop inks that provide high qualityprints on a wide variety of recording media, including plain paper.Particularly, there is a great need to develop dye-based inks which havehigh optical densities on receivers and also superior lightfastness andcolorfastness. These and other needs may be achievable in embodiments ofthe present invention.

Oil soluble (water insoluble) dyes have been studied to achieve theserequirements. Some inks use organic solvents, but such inks haveenvironmental considerations. Water-based oil soluble dye inks have theadvantages of low pollution, low price, and good quality. It isdifficult, however, to form a stable dispersion of oil soluble dye inwater media. WO 98/14524 and U.S. application Ser. No. 09/510,879, filedFeb. 23, 2000, disclose oil soluble colorants which have been dissolvedin organic solvents and added to aqueous polymer latexes slowly underagitation. After mixing, the organic solvent is evaporated and thecolorant is loaded to the polymer particles. The mixture is used toformulate ink jet inks with the addition of water, humectants, and someother additives. U.S. Pat. No. 5,958,998 discloses an ink compositioncontaining an oil soluble colorant. The composition is made by flushingpigment into a sulfonated polyester resin having a degree of sulfonationof about 2.5 to about 20 mol percent; dispersing the pigmented polyesterresin in water at a temperature of from about 40° C.-95° C., andthereafter separating and mixing. The dispersing is done by a shearingdevice operating at speeds of 100 to 5000 revolutions which yieldsstable pigmented submicron sized particles of from about 5 to about 150nanometers. However, the amount of colorant that may be loaded in thepolymer is limited.

JP 00297126A discloses a process for making an ink composition whereinpolymer-colorant particles are prepared using a batch emulsionpolymerization process employing colorant, monomers, and an initiator.This process, however, involves more micelle particle nucleation andpolymer particles are produced. When formulated into an ink jet ink, thepresence of free polymers (both polymer particles and water-solublepolymers) can significantly increase ink viscosity, decrease ink storagestability, cause premature printing head failure, and generate imagedefects.

U.S. Ser. Nos. 10/020,644 and 10/017,729 disclose a process for makingink jet ink composition comprising water, a humectant, and polymer-dyeparticles, wherein said polymer-dye particles comprise a colorant phasecontaining a water insoluble dye, and a polymer phase, said particlesbeing associated with a co-stabilizer. However, the ozone stability ofthe above ink on porous receivers is still not optimized.

There is still needed a colorant particle dispersion that has improvedcompatibility with water-soluble organic solvents and improved stabilityin an ink jet composition. There is further a need for an inkcomposition which, when printed, provides images on the surface of anink jet recording element having improved image quality, improvedphysical durability such as scratch and smudging resistance, andsignificantly improved image stability such as colorfastness and waterfastness.

SUMMARY OF THE INVENTION

The present invention provides an ink jet ink composition comprisingwater, a humectant, and polymer-dye particles, wherein said polymer-dyeparticles comprise a colorant phase containing a water insoluble dye,and a polymer phase, said particles being associated with aco-stabilizer, wherein said co-stabilizer is a water-dispersiblepolymeric material. In one embodiment the polymer-dye particles are madeby a process comprising, in order:

-   I) forming a colorant mixture comprising a water insoluble dye and    an organic medium containing at least one ethylenically-unsaturated    monomer;-   II) combining said colorant mixture with an aqueous mixture    comprising a surfactant and a water-dispersible polymeric    co-stabilizer to form a colorant mixture/aqueous mixture;-   III) causing the colorant mixture/aqueous mixture to form a stable    aqueous droplet mixture via strong agitation; and-   IV) initiating polymerization to form composite polymer-dye    particles comprising a colorant phase and a polymer phase;-   wherein an addition polymerization initiator is added prior to    initiating polymerization; and.

This invention further provides an ink jet printing method, comprisingthe steps of:

-   A) providing an ink jet printer that is responsive to digital data    signals;-   B) loading said printer with an ink jet recording element comprising    a support having thereon an image-receiving layer;-   C) loading said printer with an ink jet ink composition comprising    water, a humectant, and polymer-dye particles, wherein said    polymer-dye particles comprise a colorant phase containing a water    insoluble dye and a polymer phase, said particles being associated    with a water-dispersible polymeric co-stabilizer; and-   D) printing on said image-receiving layer using said ink jet ink    composition in response to said digital data signals.

The final composite polymer-dye particles utilized in the invention havebetter stability than those prepared by the prior art. The particles arealso more stable during the manufacturing process. Inks formulated withsuch particles have improved ozone stability, colloid stability, andgood resistance to abrasion.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, a colorant mixture is formedwhich comprises a water insoluble dye and an organic medium comprisingethylenically-unsaturated monomers. Generally the water insoluble dye isdissolved at room temperature in an organic medium containingethylenically-unsaturated monomers to form the colorant mixture.

A broad range of water-insoluble dyes may be used in the invention suchas an oil dye, a disperse dye, or a solvent dye, such as Ciba-GeigyOrasol Red G, Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, andCiba-Geigy Orasol Yellow. Preferred water-insoluble dyes can be xanthenedyes, methine dyes, polymethine dyes, anthroquinone dyes, merocyaninedyes, azamethine dyes, azine dyes, quinophthalone dyes, thiazine dyes,oxazine dyes, phthalocyanine dyes, mono or poly azo dyes, and metalcomplex dyes. More preferably, the water insoluble dyes can be an azodye such as a water insoluble analog of the pyrazoleazoindole dyedisclosed in U.S. patent application Ser. No. 09/689,184 filed Oct. 12,2000, incorporated herein by reference, and the arylazoisothiazole dyedisclosed in U.S. Pat. No. 4,698,651, incorporated herein by reference;or a metal-complex dye, such as the water-insoluble analogues of thedyes described in U.S. Pat. Nos. 5,997,622 and 6,001,161, bothincorporated herein by reference, i.e., a transition metal complex of an8-heterocyclylazo-5-hydroxyquinoline. The solubility of the waterinsoluble dye used in the present invention should be less than 1 g/L inwater, and more preferably less than 0.5 g/L in water.

The ethylenically-unsaturated monomers which can be used in theinvention include, for example, the following monomers and theirmixtures: acrylic acid, methacrylic acid, ethacrylic acid, methylacrylate, ethyl acrylate, ethyl methacrylate, benzyl acrylate, benzylmethacrylate, propyl acrylate, propyl methacrylate, iso-propyl acrylate,iso-propyl methacrylate, butyl acrylate, butyl methacrylate, hexylacrylate, hexyl methacrylate, octadecyl methacrylate, octadecylacrylate, lauryl methacrylate, lauryl acrylate, hydroxyethyl acrylate,hydroxyethyl methacrylate, hydroxyhexyl acrylate, hydroxyhexylmethacrylate, hydroxyoctadecyl acrylate, hydroxyoctadecyl methacrylate,hydroxylauryl methacrylate, hydroxylauryl acrylate, phenethylacrylate,phenethyl methacrylate, 6-phenylhexyl acrylate, 6-phenylhexylmethacrylate, phenyllauryl acrylate, phenyllaurylmethacrylate,3-nitrophenyl-6-hexyl methacrylate, 3-nitrophenyl-18-octadecyl acrylate,ethyleneglycol dicyclopentyl ether acrylate, vinyl ethyl ketone, vinylpropyl ketone, vinyl hexyl ketone, vinyl octyl ketone, vinyl butylketone, cyclohexyl acrylate, 3-methacryloxypropyl-dimethylmethoxysilane,3-methacryloxypropyl-methyldimethoxysilane,3-methacryloxypropyl-pentamethyldisiloxane,3-methacryloxypropyltris-(trimethylsiloxy)silane,3-acryloxypropyl-dimethylmethoxysilane,acryloxypropylmethyldimethoxysilane, trifluoromethyl styrene,trifluoromethyl acrylate, trifluoromethyl methacrylate,tetrafluoropropyl acrylate, tetrafluoropropyl methacrylate,heptafluorobutyl methacrylate, isobutyl acrylate, isobutyl methacrylate,2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isooctyl acrylate,isooctyl methacrylate, N,N-dihexyl acrylamide, N,N-dioctyl acrylamide,N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate,N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate,piperidino-N-ethyl acrylate, vinyl propionate, vinyl acetate, vinylbutyrate, vinyl butyl ether, and vinyl propyl ether ethylene, styrene,vinyl carbazole, vinyl naphthalene, vinyl anthracene, vinyl pyrene,methyl methacrylate, methyl acrylate, alpha-methylstyrene,dimethylstyrene, methylstyrene, vinylbiphenyl, glycidyl acrylate,glycidyl methacrylate, glycidyl propylene, 2-methyl-2-vinyl oxirane,vinyl pyridine, aminoethyl methacrylate, aminoethylphenyl acrylate,maleimide, N-phenyl maleimide, N-hexyl maleimide, N-vinyl-phthalimide,and N-vinyl maleimide poly(ethylene glycol) methyl ether acrylate,polyvinyl alcohol, vinyl pyrrolidone, vinyl 4-methylpyrrolidone, vinyl4-phenylpyrrolidone, vinyl imidazole, vinyl 4-methylimidazole, vinyl4-phenylimidazole, acrylamide, methacrylamide, N,N-dimethyl acrylamide,N-methyl acrylamide, N-methyl methacrylamide, aryloxy dimethylacrylamide, N-methyl acrylamide, N-methyl methacrylamide, aryloxypiperidine, and N,N-dimethyl acrylamide acrylic acid, methacrylic acid,chloromethacrylic acid, maleic acid, allylamine, N,N-diethylallylamine,vinyl sulfonamide, sodium acrylate, sodium methacrylate, ammoniumacrylate, ammonium methacrylate, acrylamidopropanetriethylammoniumchloride, methacrylamidopropane-triethylammonium chloride,vinyl-pyridine hydrochloride, sodium vinyl phosphonate and sodium1-methylvinylphosphonate, sodium vinyl sulfonate, sodium1-methylvinyl-sulfonate, sodium styrenesulfonate, sodiumacrylamidopropanesulfonate, sodium methacrylamidopropanesulfonate, andsodium vinyl morpholine sulfonate, allyl methacrylate, allyl acrylate,butenyl acrylate, undecenyl acrylate, undecenyl methacrylate, vinylacrylate, and vinyl methacrylate; dienes such as butadiene and isoprene;esters of saturated glycols or diols with unsaturated monocarboxylicacids such as, ethylene glycol diacrylate, ethylene glycoldimethacrylate, triethylene glycol dimethacrylate, 1,4-butanedioldimethacrylate, 1,3-butanediol dimethacrylate, pentaerythritoltetraacrylate, trimethylol propane trimethacrylate and polyfunctuionalaromatic compounds such as divinylbenzene and the like.

The polymer formed by the ethylenically-unsaturated monomers may be ahomopolymer, a co-polymer, or a cross-linked polymer. Preferably theresulting polymer is water insoluble. In one embodiment of theinvention, the polymer formed is a cross-linked polymer and theethylenically-unsaturated monomers which may be employed are a mixtureof monomers which comprises a) an ethylenically-unsaturated monomerbeing free of ionic charge groups and capable of addition polymerizationto form a substantially water-insoluble homopolymer, and b) anethylenically-unsaturated monomer capable of being a cross-linker. Inanother embodiment, an ethylenically-unsaturated monomer capable ofaddition polymerization to form a substantially water-solublehomopolymer may additionally be utilized to form the co-polymer or thecross-linked polymer. In one suitable embodiment, the ratio of theethylenically-unsaturated monomer to the cross-linking monomer is fromabout 97:3 to about 50:50. The ethylenically-unsaturated monomer free ofionic charge groups may comprise, for example, methyl methacrylate,ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate,hexyl acrylate, n-octyl acrylate, lauryl methacrylate, 2-ethylhexylmethacrylate, nonyl acrylate, benzyl methacrylate, 2-hydroxypropylmethacrylate, acrylonitrile, methacrylonitrile, vinyl acetate, vinylpropionate, vinylidene chloride, vinyl chloride, styrene, t-butylstyrene, vinyl toluene, butadiene, or isoprene. The water solubleethylenically-unsaturated monomer may comprise, for example,N,N-dimethyl acrylamide, acrylic acid, methacrylic acid,chloromethacrylic acid, maleic acid, allylamine, N,N-diethylallylamine,vinyl sulfonamide, sodium acrylate, sodium methacrylate, ammoniumacrylate, ammonium methacrylate, acrylamidopropane-triethylammoniumchloride, methacrylamidopropane-triethylammonium chloride,vinyl-pyridine hydrochloride, sodium vinyl phosphonate and sodium1-methylvinylphosphonate, sodium vinyl sulfonate, sodium1-methylvinyl-sulfonate, or sodium styrenesulfonate. The cross-linkingethylenically-unsaturated monomer may comprise, for example, vinylacrylate and vinyl methacrylate; dienes such as butadiene and isoprene;esters of saturated glycols or diols with unsaturated monocarboxylicacids, such as ethylene glycol diacrylate, ethylene glycoldimethacrylate, triethylene glycol dimethacrylate, 1,4-butanedioldimethacrylate, 1,3-butanediol dimethacrylate, pentaerythritoltetraacrylate and trimethylol propane trimethacrylate andpolyfunctuional aromatic compounds such as divinylbenzene, and the like.Preferred monomer types are acrylates, styrenic, and others.

The organic medium may comprise only the ethylenically saturatedmonomers or it may contain an additional solvent if the dye does nothave the required solubility in the monomers alone. The additionalsolvents used can be selected from most organic solvents, such asethers, alcohols, tetrahydrofuran, chloroform, methylene chloride,ethylene dichloride, ethyl acetate, toluene, methanol, ethanol, ethyleneglycol, diethylene glycol, triethylene glycol, etc. If a solvent isutilized, it preferably is removed after the polymerization step.

In the next step of the invention the colorant mixture is combined withan aqueous mixture comprising a surfactant and a co-stabilizer to form acolorant mixture/aqueous mixture. In accordance with the invention, theco-stabilizers used can be, for example, any of the water dispersiblepolymers, including homopolymers and copolymers.

The preferred polymeric co-stabilizers used in the invention may be anaqueous dispersible polyester such as Eastman AQ® polyesters produced bythe Eastman Chemical Company. The three polyesters, Eastman AQ 29, AQ38, and AQ 55 are composed of varying amounts of isophthalic acid,sodium sulfoisophthalic acid, diethylene glycol, and1,4-cyclohexanedimethanol. These thermoplastic, amorphous, ionicpolyesters are prepared by a melt-phase condensation polymerization athigh temperature and low pressure, and the molten product is extrudedinto small pellets. The solid polymer disperses readily in water at 70°C. with minimal agitation to give translucent, low viscosity dispersionscontaining no added surfactants or solvents. Varying the amount of ionicmonomers, i.e., sulfoisophthalic acid, can control the particle size.

The particle size of the co-stabilizer is preferably less than 100 nm,more preferably, less than 50 nm. The amount of the co-stabilizer usedcan be a 0.1:1 to 10:1 ratio to the surfactants used, and morepreferably a 1:1 to 10:1 ratio to the surfactants used. This step isnormally performed at room temperature.

Surfactants that can be used in the present invention include, forexample, a sulfate, a sulfonate, a cationic compound, a reactivesurfactant, an amphoteric compound, and a polymeric protective colloid.Specific examples are described in “McCutcheon's Emulsifiers andDetergents: 1995, North American Editor” and will be known to thoseskilled in the art.

In accordance with the invention, the colorant mixture/aqueous mixtureis mixed via strong mechanical agitation, such as by sonification,homogenation or microfluidization to form a stable aqueous dropletmixture. The duration of the mixing time depends on the types ofmonomers, colorants, and surfactants. The agitation usually can bestopped between 1 minute to 40 minutes. Detailed information about theprocess and the stabilizers can be found in “Emulsion Polymerization andEmulsion Polymers” (P. A. Lovell, M. S. El-Aasser, John Wiley & SonsLtd., England, 1997), incorporated herein by reference.

An addition polymerization initiator is introduced anytime prior topolymerization, preferably after the formation of the colorantmixture/aqueous mixture. After the formation of the aqueous dropletmixture, polymerization is initiated to form polymer dye particlescomprising a colorant phase and a polymer phase. In accordance with theinvention, a preferred way to cause an addition polymerization initiatorto form a free radical is by using heat. Depending on the types ofinitiators used, the reaction temperature can vary from about 30° C. toabout 90° C. Preferably the reaction temperature is at least 40° C., andmost preferably at least 50° C. To ensure that no free monomer ispresent, usually the reaction is continued for a time after the monomeraddition. Also, more initiator may need to be added as a scavengerduring the final stage of the reaction to increase the reactionconversion.

Addition polymerization initiators useful in the practice of theinvention include, for example, azo and diazo compounds, such as2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethyl valeronitrile),2,2′-azobis(2,3-dimethyl butyronitrile), 2,2′-azobis(2-methylbutyronitrile), 2,2′-azobis(2,3,3-trimethyl butyronitrile),2,2′-azobis(2-isopropyl butyronitrile),1,1′-azobis(cyclohexane-1-carbonitrile),2,2′-azobis(4-methoxyl-2,4-dimethyl valeronitrile),2-(carbamoylazo)isobutyronitrile, 4,4′-azobis(4-cyanovaleric acid), anddimethyl-2,2′azobis isobutyrate, or peroxide compounds, such as butylperoxide, propyl peroxide, butyryl peroxide, benzoyl isobutyrylperoxide, and benzoyl peroxide, or water soluble initiators, forexample, sodium persulfate, and potassium persulfate, or any redoxinitiators. Preferred initiators are the oil soluble initiators.Examples of particularly suitable initiators are azo, peroxide,persulfate, and redox initiators. The initiators may be used in anamount varying from about 0.2 to 4 weight percent or higher by weight ofthe total monomers. A chain transfer agent such as butyl mercaptan, mayalso be used to control the properties of the polymer formed.

The term “composite” means that the colorant particles prepared by theprocess of the invention comprise at least two physical phases, acolorant phase, free of solvent, and a polymer phase. The phase domainsare not separated apart from each other, and there are bonds orinterfaces between them. The composite polymer-dye particles preferablyhave a particle size of less than 1 μm, more preferably they have aparticle size of less than 200 nm, and most preferably they have aparticle size of less than 100 nm. It is preferred that the polymerphase has a molecular weight of greater than about 5000 and morepreferably greater than 10,000. In one suitable embodiment, thecomposite polymer-dye particles have a mean size of less than about 200nm, and the polymer phase of each particle has a molecular weight ofgreater than about 5000. The ratio of the colorant phase to the polymerphase is preferably from about 10:90 to about 90:10, and more preferablyfrom about 20:80 to about 50:50. The co-stabilizer will remainassociated with the composite polymer dye particles. Generally, theco-stabilizer is on the surface of the polymer dye particles andoperates to stabilize the particles.

While the polymer-dye particles prepared by the process of the inventiondescribed herein are illustrated for use in ink jet inks, they may alsohave other applications such as, e.g., in paints, inks for writing pens,markers, cosmetic products, etc.

In forming an ink jet ink, it is desirable to make the polymer-dyeparticles in the form of a concentrate. The concentrate is then dilutedwith an appropriate solvent to a concentration best for viscosity,color, hue, saturation density, and print area coverage for theparticular application. Acceptable viscosities for such inks, asdetermined using a Brookfield apparatus and related methods, aregenerally not greater than 20 centipoise, and are preferably in therange of about 1 to 15 centipoise.

The polymer-dye particles prepared by the process of the invention cancomprise up to about 30% by weight of an ink jet ink composition, andpreferably from about 0.05 to 15 wt. %. Co-solvents or a humectant canalso be added to the ink composition to help prevent the ink from dryingout or crusting in the orifices of the printhead. Classes of co-solventsand humectants which may be employed include, but are not limited to,monohydric alcohols with carbon chains greater than about 10 carbonatoms such as decanol, dodecanol, oleoyl alcohol, stearoyl alcohol,hexadecanol, eicosanol, polyhydric alcohols, such as ethylene glycol,alcohol, diethylene glycol(DEG), triethylene glycol, propylene glycol,tetraethylene glycol, polyethylene glycol, glycerol,2-methyl-2,4-pentanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol(EHMP),1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol and thioglycol; loweralkyl mono- or di-ethers derived from alkylene glycols, such as ethyleneglycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl ormono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether,triethylene glycol mono-methyl or mono-ethyl ether, diethylene glycoldi-methyl or di-ethyl ether, poly(ethylene glycol) monobutyl ether(PEGMBE), and diethylene glycol monobutylether(DEGMBE);nitrogen-containing compounds, such as urea, 2-pyrrolidinone,N-methyl-2-pyrrolidinone, and 1,3-dimethyl-2-imidazolidinone; andsulfur-containing compounds such as dimethyl sulfoxide andtetramethylene sulfone.

In an ink jet ink, the polymer phase composition can be selected tomaximize the compatibility of the composite particles with the organicsolvent used in the formulation, and to maximize the interaction withthe substrate where the ink is applied. The maximized compatibility withthe organic solvent produces long-term storage stability, and themaximized interaction with the substrate improves the adhesion or smudgeresistance of the image area.

Polymeric binders can also be added to an ink prepared using thepolymer-dye particles prepared by the process of the invention toimprove the adhesion of the colorant to the support by forming a filmthat encapsulates the colorant upon drying. Examples of polymers thatcan be used include polyesters, polystyrene/acrylates, sulfonatedpolyesters, polyurethanes, polyimides and the like. The polymers may bepresent in amounts of from about 0.01 to about 15 percent by weight, andmore preferably from about 0.01 to about 5 percent by weight based onthe total amount of components in the ink.

A biocide may be added to an ink jet ink composition to suppress thegrowth of micro-organisms such as molds, fungi, etc., in aqueous inks. Apreferred biocide for an ink composition is Proxel® GXL (ZenecaSpecialties Co.) at a final concentration of 0.0001-0.5 wt. %.Additional additives which may optionally be present in an ink jet inkcomposition include thickeners, conductivity enhancing agents,anti-kogation agents, drying agents, waterfast agents, dye solubilizers,chelating agents, binders, light stabilizers, viscosifiers, bufferingagents, anti-mold agents, anti-curl agents, stabilizers and defoamers.

Ink jet inks made using polymer-dye particles prepared by the process ofthis invention are employed in ink jet printing wherein liquid ink dropsare applied in a controlled fashion to an ink receptive substrate, byejecting ink droplets from plurality of nozzles, or orifices, in a printhead of ink jet printers.

Commercially available ink jet printers use several different methods tocontrol the deposition of the ink droplets. Such methods are generallyof two types: continuous stream and drop-on-demand.

In drop-on-demand systems, a droplet of ink is ejected from an orificedirectly to a position on the ink receptive layer by pressure createdby, for example, a piezoelectric device, an acoustic device, or athermal process controlled in accordance digital data signals. An inkdroplet is not generated and ejected through the orifices of the printhead unless it is needed. Ink jet printing methods, and relatedprinters, are commercially available and need not be described indetail.

Ink jet inks using polymer-dye particles prepared by the process of thisinvention can be employed in ink jet printing wherein liquid ink dropsare applied in a controlled fashion to an ink receptive layer substrate,by ejecting ink droplets from the plurality of nozzles, or orifices, ina print head of ink jet printers.

Ink-receptive substrates useful in ink jet printing are well known tothose skilled in the art. Representative examples of such substrates aredisclosed in U.S. Pat. Nos. 5,605,750; 5,723,211; and 5,789,070 and EP813 978 A1, the disclosures of which are hereby incorporated byreference.

The following examples illustrate the utility of the present invention.

EXAMPLES

The following dyes were used in the present invention:

Preparation of Polymer-Dye Particle DispersionsInventive Polymer-Dye Particle Disipersion (Dispersion I)

In a 400 ml beaker, 1 g of Dye-1 was added, and also added were 2.4 g ofstyrene, 2.4 g of butyl methacrylate, 1.2 g of divinyl benzene, and 2.0g of ethyl acetate. After the addition, the mixture was well stirred. Inanother beaker, 50 g of deionized water, 0.6 g of sodium dodecylsulfonate surfactant, and 1.0 g of AQ 55 were added and well stirred.The organic phase and the aqueous phase were agitated violently undereither sonification or microfluidizer for more than 20 minutes. Theorganic aqueous mixture was added to the reactor, and 0.09 g ofinitiator azobisisobutyronitrile (AIBN) in 1 gram of toluene was thenadded to the reactor. The reaction was allowed to continue for 4 morehours before the reactor was cooled down to room temperature. Theorganic solvent was removed under reduced pressure. The polymer-dyeparticle dispersion prepared was filtered through glass fibers to removeany coagulum. The particles made contain about 50% by weight of acolorant phase and about 50% by weight of a polymer phase. The initiatorwas added before the sonification or microfluidizer. The particle sizewas measured by a Microtrac Ultra Fine Particle Analyzer (Leeds andNorthrup) at a 50% median value. The polymer-dye particle dispersion isdesignated as Inventive Polymer-Dye Dispersion (Dispersion I). Theseresults are in Table 1.

Comparative Polymer-Dye Particle Dispersion (Dispersion C)

In a 400 ml beaker, 1 g of Dye 1 was added, and also added were 2.4 g ofstyrene, 2.4 g of butyl methacrylate, 1.2 g of divinyl benzene, and 2.0g of ethyl acetate. After the addition, the mixture was well stirred. Inanother beaker, 50 g of deionized water, 0.6 g of sodium dodecylsulfonate surfactant and 1.8 g of hexadecane were added and wellstirred. The organic aqueous mixture was added to the reactor, and 0.09g of initiator azobisisobutyronitrile (AIBN) in 1 gram of toluene wasthen added to the reactor. The reaction was allowed to continue for 4more hours before the reactor was cooled down to room temperature. Thepolymer-dye particle dispersion prepared was filtered through glassfibers to remove any coagulum. The particles made contain about 50% byweight of a colorant phase and about 50% by weight of a polymer phase.The polymer-dye particle dispersion is designated as ComparativePolymer-dye Particle Dispersion (Dispersion C). The particle size wasmeasured by a Microtrac Ultra Fine Particle Analyzer (Leeds andNorthrup) at a 50% median value. These results are also in Table 1.

The procedure used to prepare the Comparative Polymer-dye ParticleDispersion is different compared with the one used to prepare theinventive Polymer-dye Particle Dispersion in that no polymericco-stabilizer was added to the reactor.

TABLE 1 Polymer-dye Polymer Particle Particle Composition * Co- SizeDispersion (wt. ratios) Initiator stabilizer (nm) Dispersion I S/BMA/DVB(40/40/20) AIBN AQ55 78 Dispersion C S/BMA/DVB (40/40/20) AIBNhexadecane 120 Note: * BMA = butyl methacrylate; DVB = divinyl benzene;S = styrene;Ink PreparationComparative Ink 1 (Ink C-1) (Water Soluble Dye/No Polymer in Ink)

To prepare a comparative ink jet ink, 0.6 g of Control Dye 1 (10%active), 0.05 g Surfynol® 465 (Air Products Inc.), 1.2 g diethyleneglycol, 1.0 g of glycerol, and 0.3 g di(propyleneglycol) methyl ether(Dowanol® DPM) were added distilled water so that the final ink is 10.0g. The final ink contained 0.6% Control Dye-1, 0.50% Surfynol® 465, 12%diethylene glycol, 10% glycerol and 3% di(propyleneglycol) methyl ether.

Comparative Ink 2 (Ink C-2) (Water Insoluble Dye/No PolymericCo-Stabilizer)

This ink was prepared similar to Comparative Ink 1 (Ink C-1) except thatPolymer-dye Particle Dispersion C (Dispersion C) was used instead ofControl Dye 1. To prepare this ink, 5.0 g of Polymer-dye ParticleDispersion C, 0.05 g Surfynol® 465 (Air Products Inc.), 1.2 g diethyleneglycol, 0.6 g glycerol, and 0.3 g di(propyleneglycol) methyl ether(Dowanol® DPM) were added distilled water so that the final ink is 10.0g. The final ink contained 50% of the Polymer-dye Particle Dispersion C(about 10% active), 0.50% Surfynol® 465, 12.0% diethylene glycol, 6%glycerol, and 3% di(propyleneglycol) methyl ether.

Comparative Ink 3 (Ink C-3) (Water Insoluble Dye/AQ55 as Ink Additive)

This ink was prepared similar to Comparative Ink 2 (Ink C-2) except that0.32 g of AQ55 (30.9% active) was also added into the ink in addition tothe other components. The final ink contained additional 1% AQ55.

Ink of the Invention (Ink I) (Water Insoluble Dye/AQ55 as Co-Stabilizer)

Ink I was prepared similar to Comparative Ink 2 (Ink C-2) except thatthe Inventive Polymer-dye Particle Dispersion (Dispersion I was usedinstead of the Comparative Polymer-dye Particle Dispersion (DispersionC).

Elements Used in the Present Invention

Comparative Element 1 (C-1) (Water Soluble Dye/No Polymer in Ink)

The Comparative Ink 1 (Ink C-1) was filtered through a 1 μmpolytetrafluoroethylene filter and filled into an empty Epson 660 inkjet cartridge. A test image consisting of a series of 6 variable densitypatches, approximately 15 by 13 mm in size, ranging from 5% dot coverageto 100% dot coverage was printed onto commercially available EpsonPremium Glossy Paper, Cat. No SO41286, using the above ink with an Epson660 inkjet printer. The sample was allowed to dry for 24 hours atambient temperature and humidity.

Comparative Element 2 (C-2) (Water Soluble Dye/No Polymer in Ink)

Comparative Element 2 was prepared similar to Comparative Element 1except that a commercially available paper, Kodak Instant-DryPhotographic Glossy Media (Cat 8103137), was used instead of EpsonPremium Glossy Paper.

Comparative Element 3 (C-3) (Water Insoluble Dye/No PolymericCo-Stabilizer)

Comparative Element 3 was prepared similar to Comparative Element 1except that Comparative Ink 2 (Ink C-2) was used instead of ComparativeInk 1 (Ink C-1).

Comparative Element 4 (C-4) (Water Insoluble Dye/No PolymericCo-Stabilizer)

Comparative Element 4 was prepared similar to Comparative Element 3except that a commercially available paper, Kodak Instant-DryPhotographic Glossy Media (Cat 8103137), was used instead of EpsonPremium Glossy Paper.

Comparative Element 5 (C-5) (Water Insoluble Dye/AQ55 as Ink Additive)

Comparative Element 5 was prepared similar to Comparative Element 1except that Comparative Ink 3 (Ink C-3) was used instead of ComparativeInk 1 (Ink C-1).

Comparative Element 6 (C-6) (Water Insoluble Dye/AQ55 as Ink Additive)

Comparative Element 6 was prepared similar to Comparative Element 5except that a commercially available paper, Kodak Instant-DryPhotographic Glossy Media (Cat 8103137), was used instead of EpsonPremium Glossy Paper.

Element 1 of the Invention (I-1) (Water Insoluble Dye/AQ55 asCo-Stabilizer)

Element 1 of the Invention was prepared similar to Comparative Element 1except that Inventive Ink (Ink I) was used instead of Comparative Ink 1(Ink C-1).

Element 2 of the Invention (I-2) (Water Insoluble Dye/AQ55 asCo-Stabilizer)

Element 2 of the Invention was prepared similar to Element 1 of theInvention except that a commercially available paper, Kodak Instant-DryPhotographic Glossy Media (Cat 8103137), was used instead of EpsonPremium Glossy Paper.

Stability Tests

The above elements were subjected to light fade test and ozone test. Thelight fade test was done by exposing the samples to a 50 Klux highintensity daylight for 1 week. Ozone stability test was done by placingthe above elements in an ozone chamber (˜5 ppm ozone level, 50% relativehumidity) for 24 hours. The Status A reflection densities of the maximumdensity patch of the elements were measured using an X-Rite® 414densitometer before and after the ozone fade test. The percentages ofthe Status A densities retained for the 100% dot coverage patches werecalculated and are listed in Table 2.

TABLE 2 Light Stability Ozone Stability (% Retained at (% Retained at100% Dot 100% Dot Element Ink Coverage) Coverage) C-1 Ink C-1 7 5 C-3Ink C-2 20 8 C-5 Ink C-3 40 15 I-1 Ink I 67 51 C-2 Ink C-1 13 5 C-4 InkC-2 36 11 C-6 Ink C-3 50 32 I-2 Ink I 74 61

The above results show that the ink of the invention that although thereis some image stability improvement to light and ozone using inksformulated from particles prepared using a non-polymeric co-stabilizercompared with inks formulated with water soluble dye, a furthersignificant image stability improvement towards light and ozone wasachieved using inks of the present invention, as compared to inksformulated from particles prepared without the polymeric co-stabilizer,as well as to inks simply using the co-stabilizer polymer as an inkadditive.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

1. An ink jet ink composition comprising water, a humectant, asurfactant, and composite polymer-dye particles, wherein saidpolymer-dye particles comprise a colorant phase containing a waterinsoluble dye and a water-insoluble polymer phase, said particles beingassociated with a water-dispersible polyester polymeric co-stabilizer,wherein the mean particle size of the water-dispersible polyesterco-stabilizer is less than 200 nm, and wherein the composite polymer-dyeparticles are made by a process comprising the steps of: I) forming acolorant mixture comprising a water insoluble dye and an organic mediumcontaining at least one ethylenically-unsaturated monomer; II) combiningsaid colorant mixture with an aqueous mixture comprising a surfactantand said water-dispersible polyester co-stabilizer to form a colorantmixture/aqueous mixture; III) causing the colorant mixture/aqueousmixture to form a stable aqueous droplet mixture by using strongagitation; and IV) initiating polymerization to form compositepolymer-dye particles comprising a colorant phase and a water insolublepolymer phase; wherein an addition polymerization initiator is addedprior to initiating polymerization; and wherein polymer formed is across-linked polymer and the organic medium contains a mixture ofethylenically-unsaturated monomers comprising: a) at least oneethylenically-unsaturated monomer that is free of ionic charge groupsand undergoes addition polymerization to form a substantiallywater-insoluble homopolymer; and b) at least oneethylenically-unsaturated monomer that is a cross-linker.
 2. The ink jetink composition of claim 1 wherein the mean particle size ofwater-dispersible polyester co-stabilizer is less than 50 nm.
 3. The inkjet ink composition of claim 1 wherein the water insoluble dye has asolubility of less than 1 g/L in aqueous media.
 4. The ink jet inkcomposition of claim 1 wherein the water insoluble dye is a xanthenedye, anthroquinone dye, methine or polymethine dye, merocyanine dye,azamethine dye, azine dye, quinophthalone dye, thiazine dye, oxazinedye, phthalocyanine dye, mono or poly azo dye, or a metal complex dye.5. The ink jet ink composition of claim 1 wherein the water insolubledye is an azo dye or a metal complex dye.
 6. The ink jet ink compositionof claim 5 wherein the azo dye is an arylazoisothiazole dye.
 7. The inkjet ink composition of claim 5 wherein the metal complex dye is atransition metal complex of 8-heterocyclylazo-5-hydroxyquinoline.
 8. Theink jet ink composition of claim 1 wherein the composite polymer-dyeparticles have a particle size of less than 1 μm.
 9. The ink jet inkcomposition of claim 1 wherein the composite polymer-dye particles havea particle size of less than 200 nm.
 10. The ink jet ink composition ofclaim 1 wherein the ratio of the colorant phase to the polymer phase isfrom 10:90 to 90:10.
 11. The ink jet ink composition of claim 1 whereinthe addition polymerization initiator is an azo initiator, a peroxideinitiator, a persulfate initiator or a redox initiator.
 12. An ink jetprinting method, comprising the steps of: A) providing an ink jetprinter that is responsive to digital data signals; B) loading saidprinter with an ink jet recording element comprising a support havingthereon an image-receiving layer; C) loading said printer with the inkjet ink composition of claim 1; and D) printing on said image-receivinglayer using said ink jet ink composition in response to said digitaldata signals.